SPACEMAN EFFECTS: Redstone Germanium Preamp

Yet to build this myself, I quite like the idea behind this - I am partial to anything with bass / mid/high controls for guitar and a germanium transistor.  Bonus points for also including a discrete op-amp, which I've been playing with lately.

Before I looked at the schematic for this, I was playing around with modding a Boss Blues Driver to make the tone stack a real tone stack with external pots and removing the last stage, just leaving the two discrete op-amps.  This is a refined version of where I was heading, so I think I'll park that project for now. 

BOOST STAGE

The boost stage uses a LND150 MOSFET which is common on several Spaceman Effects designs.  It could just as easily have been a JFET-based boost - this is a clean boost to make up for the gain loss at the EQ stage.  A little bit of high-end is also filtered off at this stage, but nothing substantial.  You may not even hear it.

EQ 

It's a fairly standard bass / mid/high tone stack with some tweaked values.  This could be modded to typical values for Marshall or Fender, but there's a decent chance Spaceman went this way for a reason - it looks pretty balanced to me.

DISCRETE OP-AMP

It's a Boss-style discreet non-inverting op amp using two JFETS and a PNP transistor (as found in the Blues driver).  There are a couple of resistor value changes, and the PNP transistor is, of course, germanium instead of silicon - hence the germanium preamp name.  The GE transistor will add some extra flavour, but maybe not much more. 

According to the Dead End FX build docs, a 1T308B transistor is used - it makes sense to use Soviets for a pedal with a large production run.  If you don't have a 308 - try something around 70-80 hfe and low leakage (most Soviet-era transistors have low leakage)  Japanese transistors might also be a good choice.

Potential mod:  As this is just another type of op-amp - diodes can be added across the output of the op-amp and inverting input for some soft clipping.  It works on LTspice, so it should work in practice. I'm definitely going to try this.    

SPACEMAN REDSTONE GERMANIUM PREAMP - VERO LAYOUT

The layout below is missing the soft switching to save on size.  If you don't have ferrite beads, jumper it on the input, or use a low-value resistor in the power section (100ohm).  You could quite happily not use the MOSFET in the power supply section, but I had the room, so may as well keep it in.

The same layout as above, but this one is for a Soviet 1T308 transistor, which uses the less common BCE pinout, as many Soviet-era transistors do - you could always use the one above and bend the legs. Still, I find that annoying, so I made another layout to suit.

SCHEMATIC

I redrew part of the Deadend FZ schematic, as I found it difficult to picture the discreet op-amp.  I have not included the soft switching or fancy power supply in the drawing below.   

VIDEO DEMO